Overview of Post Harvest Cooling Methods

The world relies on agriculture to provide life-sustaining, nutritious, and delicious produce. However, while most people intuitively understand the importance of growing an ample supply of fresh fruits and vegetables, many people don’t understand or discount the importance of proper post-harvest cooling, storage, and transport.

Even locally grown produce will rapidly lose quality and decay if it is not successfully cooled and stored after harvest. Meanwhile consumption of more exotic foods that only grow in particular regions of the world would be completely untenable without good storage and cooling. Good storage and cooling is about much more than simply tossing the produce in a cooler or using a refrigerated truck to ship them – though these methods are often important and effective too; good post-harvest cooling requires careful judgement and the use of sophisticated methods to select the best approach for any given type of food. Let’s take a look at the most common post-harvest cooling methods.

Room Cooling

Room cooling is one of the most popular, widely understood cooling methods and it is likely what people imagine when they think of industrial produce cooling. With this method the produce to be cooled is simply placed in a refrigerated room such as a cooler and allowed to naturally acclimate to ambient temperatures. However, modern coolers are carefully designed to closely regulate temperatures, airflow, humidity and often a host of other environmental factors that give the produce their best chance at maximum preservation and shelf life. Room cooling is most effective for produce that does not need to rapidly reach its minimum cooling temperature or which has already been pre-cooled using another method. Room cooling is commonly used for crops such as potatoes, onions, and citrus.

Forced-Air Cooling

Forced-air cooling is a type of modified and expanded room cooling method. As with room cooling the produce is placed in a refrigerated room or cooler. However, forced-air cooling adds one or more fans that are designed to circulate – or force – cool air throughout the produce. This is important because it results in a much more rapid cooling than room cooling alone could accomplish, thus making it effective for produce that requires lower temperatures sooner after harvest to maintain peak quality.

An important feature of forced-air cooling is that the fans pull air through the produce rather than pushing it past them, which helps minimize associated dehydration. Nevertheless, forced-air cooling often requires close monitoring and a humidifying system to prevent dehydration. Good airflow is essential for forced-air cooling and thus the produce must not be too closely packed together. Forced-air cooling is commonly used for crops such as berries, tomatoes, bell peppers, and many more.

Hydrocooling

Hydrocooling is a type of pre-cooling method that involves rapidly submerging the produce in near freezing water. Hydrocooling is considered a “pre-cooling” method because with hydrocooling the goal isn’t to lower the produce to its final cooling temperature; the goal is to quickly remove field heat and prepare the produce for additional cooling with another method such as forced-air cooling or room cooling.

Hydrocooling is also effective to help the produce retain moisture and stay hydrated. It is extremely effective for pre-cooling, but due to the high cooling load, especially to achieve cooling at lower temperatures, it is not appropriate for total cooling. Hydrocooling is often used with berries, corn, broccoli, cauliflower, and many more.

Packing Ice

Packing ice involves physically cooling the produce by directly applying ice to it. This is an effective method of removing field heat as well as providing short-term cooling for transport or temporary display. The melting ice also hydrates the produce with is often very beneficial. Packing ice also has the advantage of being quick, easy, and simple.

However, packing ice is not appropriate for all types of produce. Some delicate produce may be physically damaged by ice or could suffer from over-hydration. Packing ice is also not efficient for longer-term cooling and storage. Packing ice is often used for spinach, green onions, leeks, Brussels sprouts, and others.

Vacuum Cooling

Vacuum cooling is a cooling method that utilizes low pressure to cool the produce through evaporative cooling. As the pressure is lowered the water evaporates thereby cooling the produce. Vacuum cooling is one of the most rapid and uniform methods of cooling as long as the produce being cooled readily releases water. It is suitable for most types of leafy greens, but not suitable for produce that has a water barrier.

Hydrovac Cooling

Hydrovac cooling is a combination of vacuum cooling and hydrocooling. Just prior to the “flash point” when the water evaporates from the produce additional cold water is added. This helps prevent dehydration and a loss of water weight. However, it is one of the most expensive methods of cooling and requires a sophisticated setup.

Selecting the best cooling method for a given type of produce is the key to maximizing the food’s quality, taste, freshness, and shelf life. Shelf life and quality retention over time naturally vary among different types of produce, but using the most effective post harvest method provides a major advantage. SEMCO/SEMCOLD LLC designs and supplies high quality, dependable industrial cooling and storage solutions that are suitable for a full range of different types of produce.